The invention covered by this application is related to devices intended for cooling electronic devices by removing heat by a flow of gas, in particular, air flow, said flow being produced by a blower.
The most widespread devices are the ones that comprise a heat exchanger represented by a heat sink, on one surface of which an electronic device (for instance, semiconductor device or computer processor) is installed, while another surface is made in the form of heat dissipating surface. The airflow is produced by a blower (axial fans may serve as a blower).
There are known devices of this typexe2x80x94see, for example, U.S. Pat. No. 5,867,365 xe2x80x9cCPU heat sink assemblyxe2x80x9d published on Feb. 2, 1999 (priority datexe2x80x94Jun. 10, 1997), Int.Cl. H05K 7/20, and U.S. Pat. No. 5,661,638 xe2x80x9cHigh performance spiral heat sinkxe2x80x9d published on Aug. 26, 1997 (priority datexe2x80x94Nov. 3, 1995), Int.Cl. H05K 7/20.
The design of the device described in U.S. Pat. No. 5,867,365 comprises an axial fan that produces a flow passing by heat exchanging channels of the heat sink. The majority of inlets to heat exchanging channels are located just opposite the axial fan""s impeller with a certain number of said channels being placed radially in relation to fan axle.
U.S. Pat. No. 5,661,638 also involves the application of an axial fan. Specific embodiment of device claimed in said patent involves such placement of heat exchanging channels of the heat sink that they are located centrally-symmetrically about the fan axle. To increase the heat exchange area, the heat exchanging channels are made of spiral-like shape and bent backwards in the direction of blower rotation. In this case the fan is installed in a recess made in the heat sink body.
In the above-mentioned designs, the axial fan produces sufficiently high air pressure. However, due to the weak airflow in the area adjacent to fan axle, the conditions for cooling the central part of the heat sink located underneath the fan are unfavorable. In this case non-uniform cooling of the heat sink and electronic device (in our case, processor) will take place. Besides, the energy of airflow outgoing from fan impeller in the axial direction is expended on deceleration and turn in motion before this airflow enters the heat exchanging channels. This fact decreases the speed of airflow passing by the heat exchanging channels, which, in its turn, doesn""t allow to obtain good conditions for heat exchange process.
Centrifugal blowers are used much more rarely in the cooling device designs for the purpose of producing airflow.
Specifically, U.S. Pat. No. 5,838,066 xe2x80x9cMiniaturized cooling fan type heat sink for semiconductor devicexe2x80x9d published on Nov. 17, 1998 (priority datexe2x80x94Dec. 16, 1996), Int.Cl. H05K 7/20 offers a design employing a centrifugal blower that is installed to the side of the heat sink. In one particular embodiment of this invention the cooling airflow passes by rectilinear heat exchanging channels of the heat sink.
However, placement of centrifugal blower to the side of the heat sink increases device size. This is so because such location of centrifugal blower leads to insufficient coordination between the direction of channel inlets and direction of airflow supplied from the blower. The loss in airflow energy results in the reduction of airflow motion speed in heat exchanging channels and in the decline of heat exchange efficiency. A portion of energy is also expended on friction against the casing, in which the blower is enclosed.
The closest analogue to the invention being claimed is an invention described in the patent of Japan No 8-195456 entitled xe2x80x9cCooler for electronic apparatusxe2x80x9d (priority datexe2x80x94Jan. 17, 1995; application for patent published on Jul. 30, 1996; Int.Cl. H01L 023/467).
Device design comprises a centrifugal fan enclosed in the casing and installed above the heat exchanging channels that are made divergent. Another heat sink surface is made so that the possibility of thermal contact with an electronic device is provided for. The inlet of the centrifugal fan faces the heat sink. The fan produces an airflow that passes by heat exchanging channels and then gets sucked into the inlet of the centrifugal fan.
Since the centrifugal fan operates by suction, there is an area in the central part of the heat sink that is poorly blown around by the airflow (which could be seen from the Fig. presented in the published patent). Therefore, cooling of the heat sink""s central part, which is the hottest, is performed ineffectively. This disadvantage results in the uneven cooling of the heat sink. To avoid uneven cooling of the heat sink, one has to raise the fan power. In addition, the device is of quite considerable height because the centrifugal fan is placed above the heat sink.
The engineering problem to be solved with the help of the invention being claimed herein is the development of a cooler for electronic devices that ensures more uniform cooling of electronic devices due to more effective cooling of the central part of the heat exchange element and the reduction of cooling device size.
Two options of addressing this problem are being claimed.
The essence of the invention in conformity with the first option consists in the following.
A cooler for electronic devices comprises a heat exchange element (i.e. heat sink) with divergent heat exchanging channels made on its one side, while its other side is made so that a possibility of thermal contact with an electronic device is provided for, and a centrifugal blower installed on the heat exchange element in such a way that it provides for the passing of cooling flow by heat exchanging channels.
The centrifugal blower is installed in the center of symmetry of heat exchanging channels. It supplies cooling flow (for instance, airflow) to the central part of heat exchange element. Since the blower impeller is located right opposite the inlets of said heat exchanging channels, the cooling flow is then supplied to channel inlets and as it moves by said channels it cools the heat exchange element down.
Since the centrifugal blower is installed at the same level as the heat exchanging channels are, the size of the device in height is reduced and the cooling flow is directed into the heat exchanging channels without energy expenditures on turning the flow (from axial direction to the radial direction). The latter is explained by the fact that flow turn is effected owing to the properties of centrifugal blower design.
The above-mentioned specific features of the device claimed herein provide for a special cooling pattern, which is characterized by the fact that the hottest part of the heat exchange element (namely, its central part) gets cooled first, and, as compared to the above-described prototype, the entire cooling process proceeds more evenly and without losses that are caused in said prototype by flow turn and friction when the cooling flow (going from the impeller) enters the heat exchanging channels. As a consequence, when using the invention being claimed one would need a blower of lesser power and size.
It is advisable that centrifugal blower be equipped with an impeller of drum type. In this case the impeller has wide enough suction hole that makes it possible to produce a powerful enough flow to cool the central part of the heat exchange element well. Besides, for a given blower capacity, a centrifugal blower with a drum-type impeller has minimal size and rotational speed as compared to centrifugal blowers with an impeller of other type.
For the purpose of increasing heat exchange area, the heat exchanging channels can be made in the form of rows of profiled elements. In particular, these elements can me made in the form of needles.
As a particular embodiment of the invention, the heat exchanging channels may be made spiral-like and bent in the direction of centrifugal blower rotation. This will provide for the prolonged contact between the airflow and heat exchange element surface.
In addition, the heat exchanging channels may be made of constant width. This will make it possible to ensure the constancy of speed at which the airflow blows the surfaces of heat exchanging channels over. Besides, making heat exchanging channels of constant width would enable one to attain the maximum xe2x80x9cdensityxe2x80x9d of heat exchanging channels on the heat exchange element surface, which would result in obtaining greater heat exchange area.
When making heat exchanging channels spiral-like or of constant width it is advisable to orient their inlets in the direction of propagation of the output flow produced by centrifugal blower impeller. In this case the best matching between the channels and incoming airflow is attained, which, in its turn, would sustain the airflow speed at the maximum possible level.
To attain improved heat exchange in the central part of the heat exchange element, the surface underneath the suction hole of the centrifugal blower may be made needle-shaped. This part of the heat exchange element is in essence located inside the centrifugal blowerxe2x80x94in the area of the main airflow. With such an arrangement of the heat exchange element there will be practically no extra losses for the flowing over the needles, while heat exchange will be improved.
Making heat exchange element underneath the blower bent out will raise the efficiency of heat exchange. Since the centrifugal blower is installed at the same level as the heat exchanging channels are, the cooling flow is directed to the heat exchanging channels without energy expenditures spent on the turn of the flow (from axial direction to the radial direction). This flow turn is made owing to the features of centrifugal blower design and shape of the heat exchange element underneath the blower. Bent part of the heat exchange element located in the central part of blower impeller has greater heat exchange surface as compared to the case when heat exchange element is made flat. Besides radial velocity component, the airflow passing along the side conical surface of the bent part of the heat exchange element has additional tangential velocity component. Thus, due to the fact that the speed at which the heat exchange surface is blown around is increased the extra rise in heat exchange efficiency is attained. In addition, the distance between the bent surface and blower inlet is decreased in this case, which fact facilitates the increase in the airflow speed in the gap between the heat exchange element and blower impeller, thus giving extra gain in cooling efficiency.
Small height of the device claimed herein represents another important engineering accomplishment. Semiconductor device or processor is installed in the recess formed by the concave part of the heat exchange element. This concave part of the heat exchange element goes into the central part of blower impeller, which fact also decreases the size.
The above-indicated specific features of device design results in the fact that cooling flow is supplied first to the central part of the heat exchange element, which is the hottest part. Cooling of this part proceeds more evenly and without losses expended on flow turn and friction when the cooling flow (going from the impeller) enters the heat exchanging channels. As a consequence, when using the present invention design with a bent central part of the heat exchange element one would need a blower of lesser power and size.
For the purpose of improving heat exchange, the surface of the bent part of the heat exchange element (i.e. the surface facing the inlet opening of the centrifugal blower) may be made profiled in such a way that a developed heat exchange surface is produced (for instance, needle-shaped surface), e form of rows of profiled elements. This part of the heat exchange element is in essence located inside the centrifugal blowerxe2x80x94in the area of the main airflow. With such an arrangement of the heat exchange element there will be practically no extra losses for the flowing over the needles, while heat exchange will be considerably improved.
To prevent additional noise caused by the pulsation of pressure of the cooling flow at the inlets of the heat exchanging channels, it is advisable to install the centrifugal blower impeller with a radial gap of no less than 0.03 d (where d is the diameter of centrifugal blower impeller) in relation to the inlets of the heat exchanging channels.
The heat exchanging channels may be covered with a plate from above. In this case the cooling airflow will propagate only along the channels.
The cooler for electronic devices in conformity with the second option is made as follows.
The device comprises a heat exchange element (i.e. heat sink) with divergent heat exchanging channels made on its one side, while its other side is made so that a possibility of thermal contact with an electronic device is provided for, and a centrifugal blower installed on the heat exchange element in such a way that it provides for the passing of cooling flow by heat exchanging channels.
A disk-type centrifugal blower with at least one disk is used in the design. The disks are installed in such a manner that the edge of disk surface facing the heat exchange element is located opposite the inlets to the heat exchanging channels.
The centrifugal blower supplies cooling flow (for instance, airflow) to the central part of the heat exchange element, which fact facilitates the effective cooling of the hottest part of the heat exchange element. Transfer of energy from blower disk to the airflow proceeds due to the friction forces.
The airflow blows the central part of the heat exchange element over not only in the radial direction, but also in the tangential one, due to which fact an additional increase in airflow speed in the central part of the device takes place and extra gain in cooling efficiency is attained.
Since the edges of blower disk surfaces facing the heat exchange element are located opposite the inlets to the heat exchanging channels, the cooling flow is supplied to said inlets and as the airflow passes by the channels it cools the heat exchange element down. The disk-type centrifugal blower generates radial component of the cooling flow, and said radial component matches the inlets to the heat exchanging channels well.
The disk-type centrifugal blower is characterized by small size (in terms of height) while being effective enough. In addition, it is also characterized by minimal noise level as compared to other types of centrifugal blowers, all other factors being equal.
The above-mentioned specific features of the device claimed herein provide for a special cooling pattern, which is characterized by the fact that the hottest part of the heat exchange element (namely, its central part) gets cooled first, and, as compared to the above-described prototype, the entire cooling process proceeds more evenly and without losses that are caused in said prototype by flow turn and friction when the cooling flow (going from the blower disk) enters the heat exchanging channels. As a consequence, when using the invention being claimed one would need a blower of lesser power and size.
In addition, the surface of at least one of the disks of the disk-type centrifugal blower (facing the heat exchange element) may be equipped with radial fins that increase the radial component of the airflow.
Besides, axial blower blades may be installed on at least one of the disks of the centrifugal blower near its central opening, said blades being attached to the disk. The blades may be installed on one disk or on several disks. Installation of axial blower blades near the central opening of the disk increases the pressure of cooling airflow in the central part of the heat exchange element with the blower capacity being the same. Such a design of the disk-type centrifugal blower coupled with installation of axial blower blades makes it possible to attain the same blower capacity with a lower number of revolutions, which fact results in additional decrease in noise level generated by the blower.
According to one of the design options, the axial blower blades may be formed by straps that secure disk on the axle of the centrifugal blower.
The heat exchange element underneath the blower may be made bent in the direction to the blower so that the bent part of the heat exchange element is located underneath the inlet of disk blower. In this case the overall size of the device is reduced (because an electronic device fits into the recess) and cooling process is improved (because the hottest central part is blown over with a portion of flow passing at a higher speed).
For the purpose of increasing the heat exchange area, the heat exchanging channels can be made in the form of rows of profiled elements. In particular, these elements can me made in the form of needles.
As a particular embodiment of the invention, the heat exchanging channels may be made spiral-like and bent in the direction of centrifugal blower rotation. This will provide for the prolonged contact between the airflow and heat exchange element surface.
In the latter case the heat exchanging channels may be made of constant width. This will make it possible to ensure the constancy of speed at which the airflow blows the surfaces of heat exchanging channels over. Besides, making heat exchanging channels of constant width would enable one to attain the maximum xe2x80x9cdensityxe2x80x9d of heat exchanging channels on the heat exchange element surface, which would result in obtaining greater heat exchange area
When making heat exchanging channels spiral-like (including the case when they are made of constant width) it is advisable to orient their inlets in the direction of the propagation of the output flow produced by centrifugal blower. In this case the best matching between the channels and incoming airflow is attained, which, in its turn, would sustain the airflow speed at the maximum possible level.
To attain improved heat exchange, the surface of the heat exchange element part facing the inlet of the centrifugal blower may be made profiled in such a way that a developed heat exchange surface is produced (for instance, it may be made needle-shaped). This part of the heat exchange element is located in the area of the main airflow. Therefore, it gets cooled effectively. With such an arrangement of the heat exchange element there will be practically no extra losses for the flowing over the needles, while heat exchange will be considerably improved.
In addition, from the inside, the heat exchanging channels may be covered with a plate from above secured to the surface of the heat exchange element. In this case the entire cooling airflow will propagate only along the channels, which fact also facilitates the improved heat exchange.